Given the altitude of the Mile High Stadium, Barack Obama gave what amounted to a political sermon on the mount when he addressed 80,000 whooping apostles in Denver, yet his message of hope and change was firmly directed to millions of undecided Americans slumped in front of their TV screens at home.

Mr Obama has become renowned for the rhetorical flourishes in his speeches but, while there were some last night, the Democratic candidate went through a raft of policy issues, albeit not too deeply, in an attempt to counter the Republican charge that he lacks judgment and experience, does not appreciate the military and will raise people's taxes.

So in the middle section of his address the Democratic candidate declared that he would actually "cut taxes for 95% of all working families", but did not spell out how he would do it.

Mr Obama briefly mentioned abortion, gun rights, gay rights and other hot-button issues without delving into tricky details.

On a few topics, he was a bit more specific. "I will eliminate capital gains taxes for the small businesses and the start-ups that will create the high-wage, hi-tech jobs of tomorrow." He also promised to invest in green technology.

Mr Obama has often been criticised for showing no passion, for seeming aloof and distant and a little too self-assured, hence one label - "no drama Obama". Yet last night it was clear that the 47-year-old senator from Illinois wanted to invest some grit into his address and answer criticism that he does not attack John McCain hard enough.

In arguably his most passionate moment, Mr Obama spoke of how Mr McCain equalled George Bush and that America could not afford another four years of failed, hardline Republicanism. He said in a sentence that ended with a shout: "Tonight, I say to the people of America, to Democrats and Republicans and independents across this great land - enough!"

One aspect that has been very noticeable during the convention has been the emphasis on America's duty and gratitude to its military. There have been several moving video clips of Iraq veterans telling their stories of sacrifice and loss and in the Denver stadium ahead of the keynote speech the Democrats paraded an array of military chiefs who declared their faith in Mr Obama as the next commander-in-chief.

The Republicans have wrapped themselves in the American flag and it was quite clear that the Democrats wanted to reclaim it for themselves. In one of his sharpest comments, Mr Obama declared: "I've got news for you, John McCain. We all put our country first," the latter phrase being the slogan of next week's Republican convention in Minneapolis-St Paul.

A major part of last's night political exercise was to explain who Mr Obama is; to show he is an ordinary American who shares ordinary American values.

Ahead of his speech we had a teary video showing how the candidate was raised by his single mother in Hawaii and how he was a brilliant lawyer who, rather than going to some big city law firm, chose instead to serve poor people in Chicago.

Intriguingly, Mr Obama's Kenyan father was barely mentioned but he paid fulsome tribute to his grandfather, who served in General Patton's army during the Second World War, and to his grandmother, who had struggled against sex discrimination at the workplace.

It was clear he was aiming to impress the two sections of America who appear less convinced by him: low-paid working women and blue-collar men.

So these were the targets when he issued a paean to measuring economic progress; not on how many homes you have - Mr McCain famously has seven - but on whether "the waitress who lives on tips can take a day off to look after a sick kid". The message was clear: I am one of you; John McCain is not.

Much of the week has taken place in the long shadow of the Clintons. Jimmy Carter, the grand old Georgian statesman, admitted there had been tensions at the beginning of the week but that after Bill and Hillary's speeches, Democrats would go home united.

Yet one has one's doubts. Mrs Clinton's call to unite behind her erstwhile rival was loud and clear but what was missing was any endorsement of the man himself.

It seemed as if she was backing him simply because he was the Democrats' choice.

Mr Clinton, meantime, was more magnanimous. Famously stung by the attacks on his wife during the primaries, he joked about how the political heat in the Democratic contest had contributed to global warming.

Importantly, his famous sulk disappeared and he praised the "sound instincts and good judgment" of Mr Obama, who would benefit from the wisdom and experience of his running mate, the veteran Delaware senator Joe Biden.

Yet one cannot help but wonder if Mrs Clinton is half hoping Mr Obama loses, so she can have another go at the presidency in 2012 when she will be 64.

At the end of his speech, Mr Obama inevitably referred to Martin Luther King's famous "I have a dream" speech, the 45th anniversary of which fell yesterday. It was interesting to see that as he touched on the subject Mr Obama quickly adopted an evangelical tone himself. He intoned: "America, we cannot turn back. Not with so much work to be done. We cannot walk alone. At this moment, in this election, we must pledge once more to march into the future."

He spoke about the American dream and fulfilling the American promise, galvanising his audience into frenzied flag-waving and the chant of: "Yes we can." He told them: "America, we are better than these past eight years. We are a better country than this."

The exhortation to change, to start anew while recapturing the sense of unity and purpose of a golden era that went before, is a powerful message.

Whether Barack Hussein Obama can reach the mountain top will depend on whether or not enough Americans are convinced that, for all his inexperience, his "sound instincts and good judgment" can win over the forces of conservatism that Mr McCain is harnessing in his own attempt to climb to the political peak that ends at 1600 Pennsylvania Avenue in Washington DC.